Abstract
One of the most prominent life-history trade-offs involves the cost of reproduction. Oxidative stress has been proposed to be involved in this trade-off and has been associated with reduced life span. There is currently an unclear relationship between oxidative cost and the reproduction-longevity trade-off. The current study, using a non-lethal and minimally invasive (only a single blood sample and no euthanasia) method, investigated whether an oxidative cost (oxidative stress) to reproduction would be apparent in two long-lived eusocial mole-rats, the naked mole-rat (NMR), Heterocephalus glaber, and the Damaraland mole-rat (DMR), Fukomys damarensis, where breeding colony members live longer than non-breeder conspecifics. We measured the direct redox balance in plasma by measuring the oxidative stress index (OSI) based on the ratio of total oxidant status and total antioxidant activity in breeders and non-breeders of both sexes, in the two species. NMR had significantly higher OSI between breeders and non-breeders of each sex, whereas DMR showed no significant differences except for total antioxidant capacity (TAC). The mode of reproductive suppression and the degree of reproductive investment in NMR may explain to some degree the redox balance difference between breeders and non-breeders. DMR show minimal physiological changes between breeders and non-breeders except for the mode of reproduction, which may explain some variations in TAC and TOS values, but similar OSI between breeders and non-breeders.
Highlights
Life history theory addresses the trade-offs that shape animal investment patterns between reproduction, somatic maintenance and longevity [1,2,3]
This study proposes that long-lived eusocial mole-rats, namely the naked mole-rat (NMR), Heterochepahlus glaber, [31, 32] and the Damaraland mole-rat (DMR), Fukomys damarensis [33,34,35], are perfect model species to investigate whether an oxidative cost to reproduction is evident, as reproduction is naturally controlled within the species, with no experimental manipulation required for individuals who do not breed
Important to indicate that NMRs demonstrated much higher oxidative stress in comparison to DMRs, this was somewhat expected as NMR have inherently high oxidative damage (TOS) for several reasons [44, 68]
Summary
Life history theory addresses the trade-offs that shape animal investment patterns between reproduction, somatic maintenance and longevity [1,2,3]. Evidence suggests that reproducing females have chronically lower oxidative damage in some species and subsequently lower oxidative stress than non-reproducing individuals [3, 23] This finding has subsequently been proposed as the oxidative shielding hypothesis, where reproducing females may resort to pre-emptive reductions in oxidative damage and/or stress during sensitive periods of reproduction (e.g. gestation, lactation). Possible reasons for these varied responses in past studies are shortcomings within the experimental setup [22,23,24]. Individuals can set their limits on reproductive effort, with several characteristics, such as body condition, hormonal profile, behaviour, food availability and glucocorticoid concentration, all of which can influence reproduction [23, 26,27,28,29,30], which is likely to vary between and within species
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